1. Field of the Invention
The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device for improving the attachment characteristic of upper and lower substrates and preventing the penetration of external moisture, and a fabrication method thereof.
2. Description of the Related Art
In recent years, many attempts to improve the display quality of flat panel displays and provide large-sized displays have been made actively. Among them, an electroluminescent device is self-luminous and displays video image by exciting fluorescent material using carriers such as electrons and holes. The electroluminescent device is mainly classified into an inorganic electroluminescent device and an organic electroluminescent device. While the inorganic electroluminescent device requires a high voltage of 100-200V, the organic electroluminescent device can be driven at a low DC voltage of 5-20V.
FIG. 1 is a schematic sectional view of a related art bottom emission type organic electroluminescent device. Specifically, FIG. 1 illustrates a sectional view of an active matrix light emitting diode (AMOLED) that operates in bottom emission fashion. For the sake of illustrative convenience, one pixel region consisting of a red (R) sub pixel, a green (G) sub pixel, and a blue (B) sub pixel is representatively shown in FIG. 1.
Referring to FIG. 1, first and second substrates 10 and 30 are arranged to face each other. A thin film transistor T and a first electrode 12 are formed on a transparent substrate 1 of the first substrate 10 in each sub pixel. An organic electroluminescent layer 14 exhibiting red, green and blue color is formed on the thin film transistor T and the first electrode 12. A second electrode 16 is formed on the organic electroluminescent layer 14. The first and second electrodes 12 and 16 playing a role in applying an electric field to the organic electroluminescent layer 14. The first substrate 10 where the organic electroluminescent layer 14 is formed is attached to the second substrate 30 by means of a seal 40.
In the bottom emission type structure, when the first electrode 12 and the second electrode 16 are respectively used as an anode and a cathode, the first electrode 12 is formed of a transparent conductive material and the second electrode 16 is formed of a metallic material having a low work function. Under this condition, the organic electroluminescent layer 14 includes a hole injection layer 14a, a hole transporting layer 14b, an emission layer 14c, an electron transporting layer 14d, and an electron injection layer 14e, which are sequentially formed on the first electrode 12.
In the emission layer 14c, light-emitting materials taking on red, green and blue colors are arranged in each sub pixel. Like this, since the first and second substrates 10 and 30 are attached to each other by means of a single seal line, the related art organic electroluminescent device has a problem that it is susceptible to moisture and foreign substance penetrated from the outside.